A major obstacle to quality of life for stroke survivors is impaired walking ability, and restoration of locomotion is an important goal. The objective of this research is to identify mechanisms contributing to impaired walking ability post-stroke. Locomotion is normally characterized by critically-timed patterns of muscle activity in the legs. However, in persons with post-stroke hemiparesis, muscle activity is abnormally timed, which contributes to slow and unsafe locomotion. The causes of abnormal locomotor muscle timing are poorly understood; however, a dominant theory is that abnormal muscle timing is due to hyperactive stretch reflexes. Another possibility is that locomotor muscle activation patterns are fundamentally reorganized. This study aims to identify the contributions of elevated stretch reflexes and reorganization of the locomotor pattern to abnormal muscle timing post-stroke. Subjects with and without post-stroke hemiparesis will participate. Using a pedaling task, the direction of locomotion will be manipulated, and cutaneous reflexes will be elicited in leg muscles. Muscle activity and cutaneous reflex amplitude will be quantified during pedaling. It is hypothesized that, if abnormal locomotor muscle timing arises from elevated stretch reflexes, abnormal muscle activity will be present during muscle lengthening, regardless of pedaling direction. If the locomotor pattern is reorganized post-stroke, direction-dependent changes in muscle timing that are related to the sequence of the biomechanical components of pedaling will be observed, and cutaneous reflex modulation will be reorganized.